Coring devices have been in use for many years to obtain specimens, either at the surface or in a subterranean well. Typical of such devices are U.S. Pat. Nos. 4,356,872; 4,518,050; 3,794,127; 4,081,040; 3,438,452; 3,064,742; 3,146,837; 2,170,716; 1,784,886; 3,139,147; 4,807,707; 2,382,992; 4,669,554; 4,310,057; 2,141,261; 4,350,051; 4,335,622; 4,804,050; and 2,740,477.
Some of these devices have incorporated a ball valve at the lower end to close off the core barrel after a sample is obtained. This feature is shown in U.S. Pat. Nos. 3,146,837; and 4,356,872. These ball valves are mounted in the tool, with the core barrel typically extending through the ball valve when the valve is in the open position to obtain the core specimen. Once the sample has been obtained and the core barrel is retracted, upon return of the core barrel into the tool, a linkage device has been employed to close off the ball valve to isolate the core barrel within the tool. This feature is also shown in U.S. Pat. No. 4,256,192, as well as in Eastman Christensen Technical Data Sheet entitled "Pressure Coring Service."
In the past, devices resembling a clam shell, referred to as full closure core catchers, have been used at the lower end of the core barrel to recover loose, soft or unconsolidated formations practically and efficiently. The core catchers are spring-loaded devices which are also helpful in gripping more consolidated formations securely and retaining them in the core barrel. Typical patents illustrating this feature are U.S. Pat. Nos. 4,606,416; 4,552,229; 4,553,613; 4,607,710; and 4,605,075; and Society of Petroleum Engineers (SPE) paper SPE-15385, entitled "Improved Coring and Core-Handling Procedures for the Unconsolidated Sands of the Green Canyon Area, Gulf of Mexico," by L. E. Whitebay of Conoco, Inc., presented at the 61st Annual Technical Conference and Exhibition of the Society of Petroleum Engineers held in New Orleans, La., Oct. 5-8, 1986.
Also generally of interest to the field of core sample taking are U.S. Pat. No. 3,163,241 and SPE paper 14297 entitled "New Technology in Tools for Recovery of Representative Cores from Uncemented Sand Formations," by G. A. Tibbitts, Drilling Research Laboratory, and S. R. Radford, then with Norton Christensen Inc. and an inventor of this apparatus. This paper was delivered at the 60th Annual Technical Conference and Exhibition of SPE held in Las Vegas, Nev., Sep. 22-25, 1985.
While there have been many different designs of coring devices available in the past, they have not addressed the issue of taking an undisturbed specimen from a formation which is not contaminated by the well fluids. The apparatus of the present invention has unique characteristics to allow it to obtain such undisturbed specimens.